Actuator, Particularly for a Motor Vehicle Parking Brake

ABSTRACT

An actuator ( 1 ), especially for a motor vehicle parking brake has a telescopic device ( 2 ) that actuates a brake cable ( 6 ), and a drive unit which is equipped with an electromechanical drive for actuating the telescopic device ( 2 ). The actuator ( 1 ) further has a displacement sensor unit for detecting the actuating travel of the telescopic device ( 2 ) as well as a force sensor unit for detecting the force applied to the brake cable ( 6 ) by the drive unit. The displacement sensor unit and the force sensor unit are disposed next to each other in or on the housing ( 3 ) of the telescopic device ( 2 ) while being separated from the brake cable ( 6 ). The assembly has a particularly simple and compact design while reducing the constructive and mounting effort required during the production of the actuator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of InternationalApplication No. PCT/EP2006/069101 filed Nov. 30, 2006, which designatesthe United States of America, and claims priority to German Application10 2006 002 062.6 filed Jan. 16, 2006, the contents of which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to an actuator, in particular for a motor vehicleparking brake, with an actuating unit comprising an electromechanicaldrive.

BACKGROUND

From prior art, for example from Document EP 0 966 376 B1, it is knownto monitor the application and release of tension on the brake cable inmotor vehicle parking brakes, in particular in electronically controlledparking brakes that have an electromechanical drive. To this end a forcemeasurement is implemented to detect the force applied to the brakecable and a distance measurement is implemented to detect adjustmenttravel of the brake cable already covered. This requires both a sensorsystem to measure the force and also a further sensor system to measurethe distance.

For force measurement, a force sensor is disposed in or on the actuatingcable for the direct detection of the force applied to the actuatingcable. The distance is measured by means of a displacement sensorassigned to the actuating cable, the signals of said displacement sensorbeing fed to the control device as input variables. In this way, thesensor signals from two sensor units that are at different positions ofthe brake cable and hence remote therefrom, even possibly outside theactual drive unit and separate from the control unit, must be broughttogether to the evaluating unit located in the control unit, for examplea processor. Complicating the matter is the fact that the sensor unitsmust move along with the stroke of the actuating cable. This requiresadditional signal lines and costly circuit work, such as, for example,the laying of flexible lines or flexible line carriers.

SUMMARY

An actuator, in particular for a motor vehicle parking brake, can beprovided with an actuating unit comprising an electromechanical driveand sensor devices for measuring the stroke and cable force. This can beof a particularly simple and compact design and may at the same timereduce the constructive and mounting effort required during theproduction of the actuator.

According to an embodiment, an actuator may comprise—a drive devicecomprising an electromechanical drive,—a telescopic device that actuatesa brake cable in a housing, which is drivingly-connected to the drivedevice,—a displacement sensor unit for detecting the adjustment travelof the telescopic device, comprising a displacement signal sensor and adisplacement signal receiver, and—a force sensor unit for detecting theforce applied to the brake cable by means of the telescopic device,comprising a force signal sensor and a force signal receiver, whereinthe displacement sensor unit and the force sensor unit being disposedspatially adjacent to each other in the housing of the telescopic deviceand separate from the brake cable.

According to a further embodiment, the displacement signal sensor andthe force signal sensor may be combined in one assembly. According to afurther embodiment, the displacement signal sensor and the force signalsensor may be combined in one single component. According to a furtherembodiment, the telescopic device may have a hollow shaft and a spindleshaft axially connected to said hollow shaft in a manner that enables itto rotate and advance as well as a drive gear wheel, which in respect ofrotation and axial displacement is fixed to the hollow shaft in adefined fashion and which is drivingly-connected to theelectromechanical drive, wherein the telescopic device in its housingbeing axially mounted in a movable fashion along the longitudinal axisof the actuating unit and being supported against the housing with aspring element. According to a further embodiment, the force signalsensor and/or the displacement signal sensor may be disposed on thehollow shaft. According to a further embodiment, displacement signalreceiver and force signal receiver can be disposed adjacent to eachother on a common support unit in or on the housing of the telescopicdevice in such a way that they can pick up the sensor signals fromdisplacement signal sensor and force signal sensor. According to afurther embodiment, the support unit may be a circuit support, on whichfurther components of an electronic control unit of the actuator aredisposed. According to a further embodiment, the displacement signalsensor can be a rotational travel sensor, which transmits one or severalsignals proportional to the rotational travel of a drive element to thedisplacement signal receiver or generates said signals with the helpthereof. According to a further embodiment, the force signal sensor canbe a translation displacement sensor, which transmits one or severalsignals proportional to a translational movement of the telescopicdevice against the spring element to the force signal receiver orgenerates said signals with the help thereof. According to a furtherembodiment, the force signal receiver and/or the displacement signalreceiver may have a Hall element.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below withreference to exemplary embodiments, which are described with the help ofthe drawings, in which;

FIG. 1 shows a longitudinal section of a first embodiment of anactuator,

FIG. 2 a shows an enlarged detailed view from FIG. 1,

FIG. 2 b shows the detail from FIG. 2 in a further embodiment,

FIG. 3 shows a cross-section of the actuator from FIG. 1,

FIG. 4 shows a perspective sectional view of the actuator from FIG. 1,

FIG. 5 shows a longitudinal section of the second embodiment of anactuator,

FIG. 6 shows an enlarged detailed view from FIG. 5,

FIG. 7 shows a perspective view of the actuator from FIG. 5.

DETAILED DESCRIPTION

The actuator according to an embodiment includes a drive devicecomprising an electromechanical drive and a telescopic device thatactuates a brake cable, said telescopic device is in a housing and isdrivingly-connected to the drive device. In addition the actuator has adisplacement sensor unit for detecting the adjustment travel of thetelescopic device with a displacement signal sensor and a displacementsignal receiver, as well as a force sensor unit for detecting the forceapplied to the brake cable by means of the telescopic device with aforce signal sensor and a force signal receiver. There the displacementsensor unit and force sensor unit are disposed spatially adjacent toeach other in the housing of the telescopic device and separate from thebrake cable.

According to various embodiments, the sensor units that were previouslyseparate from each other and separate from the control unit may bereplaced by a solution that cuts down on space and mounting effort. Tothis end, the displacement sensor unit and the force sensor unit aredisposed adjacent to each other in the area of the telescopic device inor on the housing of the telescopic device. As this means that noadditional housing or support components are required for the sensorunits and for the signal line, then compared with the known solution,not only is the required installation space reduced but also the numberof components and hence the effort required for mounting and the risk oferrors.

In one embodiment, the displacement signal sensor and the force signalsensor are designed as a functional assembly. This has the advantagethat the complete transmitter assembly can be pre-assembled in onepre-assembly step and built in as a unit in the final assembly. Thecommon positioning of the two signal sensors together reduces additionalmeasuring inaccuracies in terms of distance or force measurement as aresult of faulty positionings.

In a further advantageous development, the displacement signal sensorand the force signal sensor are combined in a single component. In otherwords, only one single signal sensor is provided, which interacts bothwith the displacement signal receiver and also with the force signalreceiver. This further reduces the space requirement and the productionand mounting effort.

The axially guided movable arrangement of the telescopic device in ahousing or similar on the longitudinal axis of the actuating unit isparticularly advantageous, with the telescopic device having a hollowshaft and a spindle shaft that is axially connected to said hollow shaftin a manner that enables it to rotate and advance, and also a drive gearwheel. The drive gear wheel is attached to the hollow shaft and is fixedin respect of the rotation and axial displacement of said hollow shaft.The telescopic device is drivingly-connected to the electromechanicaldrive via the drive gear wheel.

The telescopic device is mounted in an axially movable fashion in itshousing along its longitudinal axis and the longitudinal axis of theactuating unit and is supported against the housing by means of a springelement.

This embodiment has the advantage that the essential function elementsare disposed spatially close to each other thus enabling the actuator tobe of a very compact design.

In a further development of the above-mentioned arrangement, the forcesignal sensor and/or the displacement signal sensor are likewisedisposed on the hollow shaft of the telescopic device. In this way thesignal sensors are assigned directly to the central unit, which providesrelevant, proportional and measurable variables in the form ofrotational or translational movement both for distance measurement andalso for force measurement purposes. This is a simple method of enablingthe two sensor units to be disposed very close together.

A further advantageous effect is achieved if the displacement signalreceiver and force signal receiver are disposed adjacent to each otheron a common support unit in or on the housing of the telescopic device.The support unit can be designed as a lead frame, as a printed circuitboard, as a housing part or as similar functional part. The arrangementof the support unit is chosen so that the displacement signal receiverand the force signal receiver operatively interacts with the signalsensors and can pick up the sensor signals from the displacement signalsensor or from the force signal sensor. This then also presents thepossibility of combining and placing the signal receivers on oneassembly and in one pre-assembly step. In the final assembly, only aninstallation and adjustment process is still required.

In a development of the above-mentioned embodiment, a circuit support,in particular a circuit board, is used as a support unit. Furthercomponents of an electronic control unit of the actuator are disposed onthis circuit support in the same way as the signal receivers. This isadvantageous in that the electronic components required to evaluate andfurther process the sensor signals can be disposed directly adjacent tothe sensor units and can be electrically interconnected with each other.If necessary, the complete control electronics for the actuator can thusbe accommodated on this circuit support and with said circuit support inthe common housing with the telescopic device. This results in aparticularly compact design and in addition the possibility of combiningall the necessary electronics on one assembly and in one manufacturingprocess. As already mentioned above, the hollow shaft of the telescopicdevice is particularly suitable for this.

In an embodiment, the displacement signal sensor of the displacementsensor unit is designed as a rotational travel sensor, which transmitsone or several signals proportional to the rotational travel of a driveelement to the displacement signal receiver or generates said signalswith the help thereof. This can be, for example, a sensor wheel withregular toothing on its perimeter interacting with an active Hall sensorelement, a slotted or perforated disk interacting with a light barrier,a magnetic wheel magnetized with alternating polarity interacting with apassive Hall sensor element, a rotary potentiometer or another solutionfor measuring a relative or absolute rotational travel known to theperson skilled in the art. The rotational travel sensor is connected toany rotating functional part of the drive unit or of the geartransmission including the telescopic device, the number of revolutionsof which functional part is proportional to the stroke of the telescopicdevice. Preferably a functional part is chosen for this that is disposedin the vicinity of the force sensor unit. This enables the actuator tobe of a particularly compact design.

A further advantageous embodiment is characterized in that the forcesignal sensor is a translation displacement sensor, which transmits oneor several signals proportional to a translational movement of thetelescopic device against the spring element to the force signalreceiver or generates said signals with the help thereof. In this casethrough the spring constant of the spring element, for example a spiralspring, an unequivocal connection between the displacement traveledagainst the spring element and the force generated can be used in orderto determine the tractive force generated. In principle, any type ofdistance or displacement measurement can be used. Examples of this areinductive distance measurement, linear potentiometer or also opticaldistance measurement. Such an embodiment represents a particularlysimple and robust type of force measurement. In addition when combinedwith a rotational travel sensor for determining the adjustment travel asdescribed above this offers the possibility of determining both thevariables that are to be measured on one component of the actuatingunit, namely of the hollow shaft of the telescopic device. Thereby therotation of the hollow shaft provides a measurement for the adjustmenttravel and the translatory motion for the actuating force.

A particularly simple and robust embodiment in respect of the sensorunits is produced when the force signal receiver and/or the displacementsignal receiver has a Hall element. Hall elements react to magneticfields and can be designed both as so-called active or prestressedsignal receivers as well as passive signal receivers. In the first case,the Hall element is permanently applied with a magnetic field. Theassociated signal sensor generally consist of a ferromagnetic materialand moves within the magnetic field which results in a change beinggenerated in the magnetic field, which change can be measured using theHall element. In the passive design, the Hall element is applied with amagnetic field by a signal sensor that has magnetization, said magneticfield changing when the signal sensor moves in relation to the Hallelement. This change can again be measured using the Hall element.

FIG. 1 shows an actuator 1 in the form of an actuator for a motorvehicle parking brake, wherein an axially movable telescopic device 2 isaccommodated by a housing 3 with an axially closing housing cover 4. Thetelescopic device 2 comprises a hollow shaft 5 and a spindle shaft 7which is axially connected to said shaft in a manner that enables it torotate and advance, actuates a brake cable 6 and is connected at itsleft end with the brake cable 6.

When driving the telescopic device 2 in terms of a movement of the brakecable 6 towards the right, i.e. in terms of applying a motor vehicleparking brake (not shown in detail here), there occurs thereby an axialtranslatory motion of the spindle shaft 7 towards the right as shown inFIG. 1, wherein FIG. 1 shows a brake position when the brake cable isunder tension. A torque is transferred from an electric motor of a drivedevice (not shown) via a transmission (not shown in more detail) to adrive gear wheel 8 in the form of a gear wheel. In relation to rotationand axial translation, the drive gear wheel 8 has a rigid driveconnection to the hollow shaft 5 and can be moved together with saidshaft axially relative to the housing 3. The hollow shaft 5, rotated bythe drive gear wheel 8, has an internal thread 9. By means of thisinternal thread 9, the spindle shaft 7 produces an axial advancemovement using the intermeshing external thread 10 of the spindle shaft7.

The hollow shaft 5 or the spindle shaft 7 is concentrically encompassedby a spring element 11, here in fact a helical spring. Said helicalspring lies as a pressure spring with its one axial end over a fixedaxial thrust bearing 12 against a shoulder 13 of the housing 3 and withits other axial end against a signal sensor element 14. When theactuator is applied or released, the signal sensor element 14 disposedon the hollow shaft 5 moves with the hollow shaft 5 axially to the leftor to the right parallel to the longitudinal axis 31 of the actuator 1.The travel covered thereby is detected with the help of a fixed,stationary signal receiver, represented here by the force signalreceiver 15, and presents a measurement for the tensioning force orbrake force applied to the brake cable 6 by the drive device via thedrive gear wheel 8, the hollow shaft 5 and the spindle shaft 7. In otherwords, this travel information from the signal sensor element 14 allowsconclusions to be drawn as to the applied cable force.

The signal sensor element 14, which, when the actuator 1 is activated,rotates together with the helical spring 11 around the spindle axis 16,has a magnet 17, which, interacting with a Hall element 18 in the forcesignal receiver 15, enables the distance between the signal sensorelement 14 and Hall element 18 to be detected (cf. FIG. 2 a). The signalsensor element 14 has a circumferential collar 19, the distance 20 ofwhich from the Hall element 18 serves as a measurement for the forceapplied to the brake cable 6.

Instead of the above-mentioned embodiment, one can also use a so-calledprestressed force signal receiver 15′, which includes a magnet 33 inaddition to the Hall element 18′ in the sensor element housing 32, cf.FIG. 2 b. The movement of a signal sensor element 14′, which is producedfrom a ferritic material or is a ferrite, causes a change in themagnetic field.

In the direct vicinity of the Hall element 18 of the force signalreceiver 15, 15′ and on the same circuit support 21, here a circuitboard, as said Hall element, a further sensor element is disposed, thedisplacement signal receiver 22 for detecting the adjustment travel. Theposition of this displacement sensor receiver 22 is chosen in such a waythat, while the actuator 1 is being activated, the teeth 23 disposed onthe perimeter of the collar 19 are directed past and in the immediatevicinity of the signal sensor element 14. This allows a specific numberof pulses to be detected per rotation, i.e. the rotational travel of thesignal sensor element 14, cf. FIG. 3, which depicts a section throughthe actuator along line III-III. In other words the adjustment travel isdetected in such a way that counted pulses are assigned to therotational travel of the signal sensor element 14 covered and again therotational travel is proportional to the adjustment travel of thetelescopic device. Use is made here on the one hand of a displacementsignal receiver 22 with a Hall element 18 and on the other hand of adisplacement signal sensor 14 manufactured from a magnetic material orhaving a magnet. As an alternative to this assembly, a displacementsignal receiver 22′ with an active Hall element and a ferritic signalsensor element 14′ can also be used.

As the force signal receiver 15 and displacement signal receiver 22 areoperated via one and the same signal sensor element 14, which is axiallymovable in respect of the spindle axis 16 and can be rotated around thespindle axis 16, the circuit support 21 must be aligned solely to theposition of the spindle axis 16. In contrast, the relative position ofthe circuit support 21 in respect of the motor axis 24 for example isirrelevant. The circuit support 21 is thereby accommodated andpositioned in a corresponding receiving chamber 25 of the housing 3.

FIG. 4 shows a perspective view of the described exemplary embodiment,with the housing 3 and telescopic device 2 and also spring element 11,signal sensor element 14 and drive gear wheel 8 being intersectedlongitudinally.

FIG. 5 shows a second embodiment. Instead of a signal sensor elementprovided jointly for force signal receiver 15 and displacement signalreceiver 22, a force signal sensor 26 and a displacement signal sensor27 are provided, which are combined into one assembly and connected toeach other via an axial roller bearing 28, as is also illustrated inFIG. 7. When the actuator 1 is activated, the force signal sensor 26 andspring element 11 do not rotate along with the hollow shaft 5. This isadvantageous in that any wobbling motions of the force signal sensor 26caused by its rotational movement are avoided and hence the measurementaccuracy is improved.

With this embodiment, the force signal receiver 15 for determining forceand the displacement signal receiver 22 for determining the adjustmenttravel are disposed in direct vicinity to each other on a common supportelement 21, a circuit board. FIG. 5 shows the state of a released brakecable 6, where the brake cable has traveled to the left. The forcesignal sensor 26 with magnet 17 applied by the spring element 11 is usedto determine the force affecting the brake cable 6 using a displacementmeasurement by means of a Hall element 18 in the force signal receiver15. The spring element 11 is supported directly on the housing shoulder13.

The displacement signal sensor 27, in interaction with the displacementsignal receiver 22, assumes the function of displacement determination,for which purpose it also has teeth 23 disposed on the perimeter of thecircumferential collar 19. A magnetic wheel that has magnetized segmentsof alternating polarity can be used instead of the toothed displacementsignal sensor 27. In this way, the rotational travel is detected by thenumber of pole changes from “North Pole and South Pole” moving past thedisplacement signal receiver 22. This also applies to the common signalsensor element 14 according to the embodiment described above.

Here again, active (prestressed) as well as conventional passive Hallelements can be used for displacement signal receivers and/or forcesignal receivers. Depending on the application requirements a mixed usecan also be provided, for example, such that the force sensor unitoperates with a prestressed Hall element, while a passives Hall elementis used for the displacement sensor unit.

In both embodiments, the force signal receiver 15 and displacementsignal receiver 22 are provided on the circuit support 21 preferably asSMD modules (Surface Mounting Device). The Hall element 18 is designedhere as an integrated circuit (Chip). In addition to further componentssuch as capacitors 29 and relays 30, an evaluation and control circuit(not shown) can be disposed on the circuit board 21, which evaluationand control circuit is used to detect and further process the sensorsignals and to control the actuator. The evaluation of the force ordistance measurement is preferably used to control the drive device ofthe actuating unit by means of the control unit that is also disposed onthe circuit support 21. When arranging the circuit support 21 in thehousing 3, priority is given to using up existing free spaces so thatthe installation space required is as a whole minimized.

When evaluating the signals and processing them further into concreteadjustment travel and actuating force information, it should be notedthat the adjustment travel variable, determined from the angularmomentum, must be corrected on the basis of the detected distanceinformation of the force sensor unit. This is necessary because thehollow shaft 5 of the telescopic device 2 moves axially against theadjustment travel of the brake cable 6 when the force increases and thedrive device continues to be activated. This travel covered by thehollow shaft 5 against the spring element 11 must be deducted from theadjustment travel corresponding to the angular momentum count.

According to various embodiments, neither the force sensor unit nor thedisplacement sensor unit are coupled to the brake cable, and, inaddition, are also not integrated into the force transmission path fromthe electromechanical drive up to the brake cable. Therefore, the sensorunits can be positioned at various selectable positions in the drive ortransmission unit and be fixed in these positions. This allows theactuator to be of a particularly compact design. A miniaturization ofthe force sensor unit is also possible, as the mechanical load issignificantly reduced or completely non-existent. This also contributesto a comparatively compact design.

Instead of sensor units based on a magnetic measurement principle, othersensor principles, for example a system based on optical scanning orsimilar, can also be used.

1. An actuator comprising a drive device comprising an electromechanicaldrive a telescopic device that actuates a brake cable in a housing,which is drivingly-connected to the drive device, a displacement sensorunit for detecting the adjustment travel of the telescopic device,comprising a displacement signal sensor and a displacement signalreceiver and a force sensor unit for detecting the force applied to thebrake cable by means of the telescopic device, comprising a force signalsensor and a force signal receiver, wherein the displacement sensor unitand the force sensor unit being disposed spatially adjacent to eachother in the housing of the telescopic device and separate from thebrake cable.
 2. The actuator according to claim 1, wherein thedisplacement signal sensor and the force signal sensor are combined inone assembly.
 3. The actuator according to claim 1, wherein thedisplacement signal sensor and the force signal sensor are combined inone single component.
 4. The actuator according to claim 1, wherein thetelescopic device has a hollow shaft and a spindle shaft axiallyconnected to said hollow shaft in a manner that enables it to rotate andadvance as well as a drive gear wheel, which in respect of rotation andaxial displacement is fixed to the hollow shaft in a defined fashion andwhich is drivingly-connected to the electromechanical drive, wherein thetelescopic device in its housing being axially mounted in a movablefashion along the longitudinal axis of the actuating unit and beingsupported against the housing with a spring element.
 5. The actuatoraccording to claim 4, wherein the force signal sensor and/or thedisplacement signal sensor disposed on the hollow shaft.
 6. The actuatoraccording to claim 1, wherein displacement signal receiver and forcesignal receiver are disposed adjacent to each other on a common supportunit in or on the housing of the telescopic device in such a way thatthey can pick up the sensor signals from displacement signal sensorforce signal sensor.
 7. The actuator according to claim 6, wherein thesupport unit is a circuit support, on which further components of anelectronic control unit of the actuator are disposed.
 8. The actuatoraccording to claim 1, wherein the displacement signal sensor is arotational travel sensor, which transmits one or several signalsproportional to the rotational travel of a drive element to thedisplacement signal receiver or generates said signals with the helpthereof.
 9. The actuator according to claim 1, wherein the force signalsensor is a translation displacement sensor, which transmits one orseveral signals proportional to a translational movement of thetelescopic device against the spring element to the force signalreceiver or generates said signals with the help thereof.
 10. Theactuator according to claim 1, wherein the force signal receiver or thedisplacement signal receiver has a Hall element.
 11. The actuatoraccording to claim 1, wherein the force signal receiver and thedisplacement signal receiver has a Hall element.
 12. The actuatoraccording to claim 1, wherein the actuator is part of a motor vehicleparking brake system.
 13. An method for operating an actuator comprisingthe steps of: providing a drive device comprising an electromechanicaldrive actuating a brake cable in a housing by a telescopic device,wherein the brake cable is drivingly-connected to the drive device,detecting the adjustment travel of the telescopic device by adisplacement sensor unit comprising a displacement signal sensor and adisplacement signal receiver, and detecting the force applied to thebrake cable by means of the telescopic device by a force sensor unitcomprising a force signal sensor and a force signal receiver, whereinthe displacement sensor unit and the force sensor unit being disposedspatially adjacent to each other in the housing of the telescopic deviceand separate from the brake cable.
 14. The method according to claim 13,wherein the displacement signal sensor and the force signal sensor arecombined in one assembly or in one single component.
 15. The methodaccording to claim 13, wherein the telescopic device has a hollow shaftand a spindle shaft axially connected to said hollow shaft in a mannerthat enables it to rotate and advance as well as a drive gear wheel,which in respect of rotation and axial displacement is fixed to thehollow shaft in a defined fashion and which is drivingly-connected tothe electromechanical drive, wherein the telescopic device in itshousing being axially mounted in a movable fashion along thelongitudinal axis of the actuating unit and being supported against thehousing with a spring element.
 16. The method according to claim 15,wherein the force signal sensor and/or the displacement signal sensor isdisposed on the hollow shaft.
 17. The method according to claim 13,wherein displacement signal receiver and force signal receiver aredisposed adjacent to each other on a common support unit in or on thehousing of the telescopic device in such a way that they can pick up thesensor signals from displacement signal sensor and force signal sensor.18. The method according to claim 17, wherein the support unit is acircuit support, on which further components of an electronic controlunit of the actuator are disposed.
 19. The method according to claim 13,wherein the displacement signal sensor is a rotational travel sensor,which transmits one or several signals proportional to the rotationaltravel of a drive element to the displacement signal receiver orgenerates said signals with the help thereof.
 20. The method accordingto claim 13, wherein the force signal sensor is a translationdisplacement sensor, which transmits one or several signals proportionalto a translational movement of the telescopic device against the springelement to the force signal receiver or generates said signals with thehelp thereof.